New Research Shows Baltimore Heatwave Was Worsened by DC's Hot Air

In July of 2007, the East Coast was slammed by a record-setting heat wave. From New York City to Washington, DC, temperatures averaged above 90 degrees Fahrenheit, causing more than 40 deaths.

Now, new research is demonstrating that the temperatures and poor air quality in Baltimore during this period were intensified by neighboring Washington, DC.Comparing conditions during the heat wave in both Washington, DC, and Baltimore, a clear discrepancy arises. Despite being little more than 60 miles from each other, temperatures in Baltimore were much higher, averaging 99.5 degrees Fahrenheit, than in DC, where temperatures averaged 97.7 degrees. More significantly, ozone levels in Baltimore reached 125 parts per billion, while levels in Washington peaked at 85 ppb. The amount of small particulate pollutants was also greater in Baltimore.

The reason for this, Dr. Da-Lin Zhang, a meteorologist at the University of Maryland, suggests, is the urban heat island effect. A well-known phenomenon, the heat island effect occurs when built-up urban environments create hotter temperatures than surrounding rural areas. Though this is not a new idea, Zhang's argument that the heat island created by Washington, DC, impacted temperatures in a neighboring city, is.

Commenting on the research, Susanne Grossman-Clarke, from the Global Institute of Sustainability at Arizona State University, explained, "urban planners only think about the local aspect of the heat island...[but] the city is in the context of other cities." In this case, prevailing winds carried hot air from Washington. When the air reached Baltimore it was stopped by breezes coming from the Chesapeake Bay, causing the heated air to stagnate.

After building a weather model, Zhang tested the impact of bulldozing Washington, DC, and replacing it with trees. The result was a 25% decrease in the heat island effect and a near five degree drop in temperature.

"The urban heat island is a well-known phenomenon, but was thought to be quite local," commented Gabriele Curci, a climate scientist at the University of L'Aquila in Italy. Russell Dickerson, a co-author of the study, commented that "a little state like Maryland can't do much to help global climate change, but there are things you can do to mitigate the adverse impacts of climate locally."

Local thinking, it turns out, should include cooperation with our neighbors, even if they are a city away.